Process for the production of organo sulfur compounds



United States Patent Ofiice 3,012,077 Patented Dec. 5, 1961 8 Claims.01. 260608) This invention relates to a novel method for preparing alkylorganic sulfur compounds having from 2 to 30 carbon atoms in the alkylgroups.

More specifically, the instant invention deals with a method ofproducing compounds such as alkyl hydrosulfides, alkyl sulfides, alkyldisulfides and alkyl polysulfides by reacting trialkyl aluminumcompounds with elemental sulfur to form aluminum derivatives of alkylorgano-sulfur compounds and then treating the aluminum derivatives withaqueous mineral acids. The alkyl organo-sulfur compounds can then berefined by conventional procedures.

In one modification of the above technique on alkyl sulfide is produceddirectly by reacting a trialkyl aluminum compound with an aluminummercaptide of the formula:

whereR is an alkyl group containing 2-30 carbon atoms.

The present invention provides a convenient, efficient and economicalmethod for the production of alkyl organic sulfur compounds. Thesecompounds are well known in the art and have been used as acceleratorsin the manufacture of rubber, as short-stop agents and as lubricant andfuel additives. The mercaptans, which are prepared by the instantprocess, haveadditional uses as oxidation inhibitors in hair wavingpreparations, and in the preparation of detergents.

The preferred embodiment of this invention is the twostep process;namely, reacting a trialkyl aluminum with sulfur, and then treating thereaction product with a mineral acid.

While not wishing to be bound by any theoretical considerations, itwould appear that the reaction between the trialkyl aluminum and sulfurtakes place in the following manner:

some of the aluminum thioalkyl then reacts with more trialkyl aluminumand more sulfur in the following manner:

and simultaneously, some of the aluminum thioalkyl reacts with moresulfur to yield complex aluminum polythioalkyl compounds containing manysulfur atoms. This reaction is illustrated in the following manner:

I Al(SR) +3(xl)S- Al(S R) where x -is an integer of from It is pointedout that the above formula is not intended to represent a'true chemicalequation since the exact structure of the higher molecular weightaluminum polythiolalkyls is not accurately known. This formula is merelyintended to illustrate that the sulfur further reacts with Al(SR) toproduce higher molecular weight compounds. I

As has been previously stated, the reaction mixture is then treated withan aqueous mineral acid to liberate the organic sulfur compounds. Itwouldv appear that this 2-100, preferably from reaction can beillustrated by each of the following two equations:

The sulfur compounds may be purified by distillation and may also beinterconverted with relative ease. For example, rnercaptans can beoxidized to disulfides:

2RSH+ 1 20-) RSSR+H O polysulfides can be pyrolyzed to disulfides:

and sulfides may be prepared from mercaptans and aldehydes at 2500 psi.and C. under hydrogen.

Preparation of alkyl sulfur compounds via mercaptans is well known inthe art. Mercaptan synthesis and other known processes of producingalkyl sulfur compounds produce more than one specific type of sulfurcompound. Iuterconversion of sulfur products must be relied upon toincrease the yield of the desired alkyl sulfur compound. In addition,prior known processes generally require more expensive raw materialssuch as alkyl halides, sulfates, and alcohols as a source of sulfur oras a source of the organic moiety. Many of these raw materials are notreadily available nor as easily synthesized as the correspondingalkyl-aluminum compounds used in this invention.

Many methods of synthesizing aluminum alkyls are well known. For thepurposes of this invention, the alkylaluminum compound may be derivedfrom any desired source which produces an aluminum alkyl with 2-30carbon atoms per radical. Preparation of the starting aluminum alkyldoes not form a necessary part of this invention. All aluminum alkylbonds will react with sulfur to form alkyl sulfur compounds.

In the preferred embodiment of this invention any aluminum trialkyl ormixture of trialkyls obtainable by direct synthesis is reacted withelemental sulfur to form the aluminum derivative of the organo-sulfurcompound. Typical examples of such compounds are: triethylaluminum,tripropylaluminum, tributylaluminum, triisobutylaluminum,trihexylaluminum, trioctylaluminum, trinonylaluminurn,tribenzylaluminum, tridodecylaluminurn, and trieicosylaluminum.

The alkyl group on the aluminum need not be primary. Secondaryalkylaluminum compounds can be used as a source of alkyl bonds. Branchedalkyl compounds, such as tri(2-methylpentyl) and tri(2-ethylhexyl) canalso be used as starting compounds in the preparation of alkyl sulfurcompounds. From triethylaluminum, long chain alkyls can be formed byethylene addition. Triethylaluminum can be reacted with ethylene to formtrihexyl-,' trioctyl-, tridodecyl-, etc. up to 30 carbon atoms by themethod ofZiegler, Petroleum Refiner, 34, 111-15 (1955). The productsfrom such a growth reaction may not be uniform and may in- .clude alkylsof several molecular Weights. When such an alkyl mixture containingdifferent carbon atoms is sulfurized in accordance with. the presentinvention th e resulting sulfur derivatives will likewise be mixed inmolecular weight.

A number of substituted alkylaluminurn compounds can be sulfurized inaccordance with the present process. Both alkylaluminum halides andhydrides have been synthesized and can be used as the source of alkylaluminum bonds,

Although examples herein given illustrate specific preparations preparedin accordance with this invention, the versatility of the presentprocess for the preparation of 3 valuable organic sulfur compounds ismade clear by the following description of the process including theprocess conditions required.

In the first step of this process elemental sulfur, generally in thesolid state, is added to the desired aluminum alkyl, with or without adiluent, at an absolute pressure of to 100 atmospheres and at atemperature in the range of to 300 C., with a preferred operating rangeof about 60 to about 150 C. Operating temperatures above about 120 C.can be used when it is desired to add molten sulfur to the aluminumalkyl for purposes of easier handling and metering. The time of reactionwill be dependent on the particular aluminum alkyl employed as well asthe temperature, pressure, and physical state of the sulfur. Generallyabout 0.1 to about 10 hours, preferably from about 0.1 to about 4 hours,is sufiicient to react all the sulfur. Although the process ofsulfurization can be satisfactorily performed without a diluent, theresultant product is so viscous that it must be diluted prior tohandling. It is therefore advisable to employ a diluent during the firststep, such a diluent is preferably an aromatic hydrocarbon such asbenzene or toluene. Any saturated hydrocarbon of the methane series ornaphthenic hydrocarbons such as hexane, heptane, cyclohexane, and thelike provide alternative satisfactory diluents. An oxygenated compoundcannot be used as a diluent inasmuch as most oxygenated compounds reactwith alkyls. For example, ethers form a complex with al'kylaluminumcompounds whichwill not react with sulfur as readily as an uncompletedalkyl. A reasonable amount of diluent used will range in the ratio of0.5 to 40 volumes per volume of aluminum alkyl.

In the second step, the resultant product of the first step orsulfurization stage containing the aluminumorgano-sulfur compound of thedesired alkyl sulfur compound or compounds is hydrolyzed to form thecorresponding aluminum salt and liberate the organo-sulfur compound.Various acidic hydrolyL ng techniques can be employed to effect thedesired result, the particular selection depending principally upon thecomposition of the sulfurization product mixture. Preferably thealuminum-organo-sulfur compound is treated with an aqueous mineral acidsuch as hydrochloric acid or sulfuric acid to effect hydrolysis withresultant formation of two layersa lower aqueous layer and an upperorganic layer. The lower aqueous layer is extracted with a diluent, andthe extract is added to the upper organic layer. The extractant ispreferably the same as the diluent used in the first step. The liberatedsulfur compounds contained in the organic layer, can be purified bydistillation, for example and interconverted as illustrated previously.

The novelty of this invention does not reside solely in the means oftreating the derivative of the organo-sulfur compound with aqueousmineral acid to liberate the organo-sulfur compound as various othermeans of hydrolyzing the alkyl sulfur compounds from the sulfurizationstage product mixture will be apparent to those skilled in the art.Rather, the present invention embodies a novel,

simple, and economical means of containing valuable organo-sulfurcompounds by reacting an aluminum compound with sulfur to produce thealuminum derivative of the organo-sulfurcompoun d'and hydrolyzing thereaction mixture product to liberate the desired organesulfur compound.This invention is further illustrated by reference to the followingexamples which are illustrative only and should not be construed aslimiting the invention which is properly defined in the appended claims.

. triisobutylaluminum (0.25 mol) was diluted with. 500

grams. of toluene which had been dried over anhydrous magnesium sulfate.To the flask were attached a motordriven stirrer, 'a reflux condenser, athermometer well,

and a screwtype solids feed metering device. The feed hopper for thesolids feeder was charged with 36.2 grams of sulfur (1.25 mols). Thesulfur was added to the toluene solution, by means of the solids feeder,over a period of 25 minutes. During the addition the temperature rosefrom 27.5 to 41 C. The flask was heated for an hour until the sulfur hadall reacted; the final temperature was 54 C. During the following hourand a quarter the reaction mixture cooled to 33 C. while being agitatedunder a nitrogen atmosphere.

The reaction product was transferred to a dropping funnel from whence itwas added dropwise to 300 ml. of 6 percent sulfuric acid in a stirredflask. The addition took place over a period of 20 minutes during whichthe temperature rose from 27 to 57 C. The hydrolyzed product existed intwo layers: a lower aqueous layer and an upper organic layer. The lowerlayer was extracted with 100-ml. of toluene, and the toluene extract wasadded to the upper layer. Analysis of this mixture showed the presenceof 6.2 grams of isobutyl mercaptan, a yield of 9.3 percent based on thetriisobutylaluminum.

The solution of sulfur compounds from this experiment was combined withthose from two similar ones and distilled to isolate other isobutylsulfur compounds. The contained isobutyl mercaptan was removed in thedistillation fractions (SS-104 C.) boiling below toluene. From themercaptan-containing material a 2,4-dinitrophenylthioether derivativewas prepared by the procedure of Best et al. [1. Am. Chem. Soc., 54,1985 (1932)]. It melted at -76.5 C.; the reported melting point is 76 C.(R. L. Shriner and R. C. Fuson, Systematic Identification of OrganicCompounds, third edition, John Wiley and Sons, New York, 1948). The nexthigher boiling fraction, toluene was removed and then three successivefractions collected were diisobutyl sulfide (thio ether), diisobutyldisulfide, and a mixture of disulfidepolysulfide. The boiling points andmicroanalytical analyses of these fractions are listed below.

Fraction A B C Boiling Range, C. at 10 mm. Hg 52-55 -88 88-100 CompoundDiisobutyl- Diisobutyl Di and sulfide Disulfide Poly- Sulfide Found,Calcu- Found, Oalcu- Found, Analysis percent lated, percent lated,percent percent percent After removal of the last fraction (still-kettletemperature 152 C. at 10 mm. Hg) the sulfur-containing residues began todecompose and the distillation was stopped.

Preparation of l-octanethiol and other octylsulfur compounds In thereaction equipment described in Example 1, above, 48 grams. (1.5 mol) ofsulfur was added to 181.8 g. (0.40 mol) of 85 percent trioctylaluminum.The addition took place with agitation over a period of *1 hour and 20minutes, during which time the temperature was raised from 50 to 132 C.by the exothermic reaction and by electrical heating. At the end of thereaction, the product was so viscous that it was diluted with l-liter ofbenzene for handling. The benzene solution was hydrolyzed as detailedabove using a solution of 60 grams of hydrochloric acid in a liter ofwater. After hydrolysis, the water layer was extracted with benzene andthat extract was combined with the original benzene layer. This combinedsolution was stripped of benzene and distilled through a 30 x 300mm.packed column. A total of 37 grams of 1 octanethiol was recovered; thisrepresents a yield of 20.8 percent, based on the trioctylaluminum. Thepurest fraction (87 percent) distilled between 63 C. at a 6 mm. and 71C. at 8 mm. of mercury. The octanethiol vapor pressure data in theliterature, indicate respective boiling points of 64 and 70 C. at thesepressures [Ellis, L. M., Jr., and Reid, E. E., J. Am. Chem. Soc. 54,1674 (1932)]. From this fraction a 2,4-dinitrophenylthioether was made;the recrystallized derivative melted at 80.0-80.6 C. The literaturevalue is 78 C. None of the higher molecular weight sulfur compounds wasisolated, but their production was in the ratio of 1.45 parts per partof the mercaptan.

EXAMPLE 3 Reaction on sulfur with trioctadecylaluminum In the manner ofthe previous examples, 48 grams (1.5 mole) of sulfur was reacted with392.2 gm. of a 73 percent solution of trioctadecylaluminum (0.36 mol).Hydrolysis of a benzene solution of the product was again accomplishedwith an aqueous hydrochloric acid solution (6 percent). The lower layerwas extracted with benzene, and the extract was added to the upperlayer. The mixture when stripped of benzene was analyzed; it contained36.3 grams of octadecanethiol, a yield of 11.6 percent.

-Air oxidation of the mixture of sulfur-containing compounds caused theformation of a precipitate judge to be the octadecyl disulfide.Recrystallization of that precipitate gave crystals which melted at61-61.5 C. The analysis of those crystals showed that they were not puredisulfide.

Calculated Found AI(SR) with sulfur and an aluminum trialkyl of theformula:

where R in both formulas represents an alkyl group having 2 to 30 carbonatoms.

2. A method of preparing alkyl sulfur compounds which comprises reactingan aluminum mercaptide of the formula:

A1(SR) with sulfur and an aluminum trialkyl of the formula where -Rrepresents an alkyl group of from 2. to 30 carbon atoms at a temperatureof from 20 to 300 C. and at an absolute pressure of from 0 to 100atmospheres, for a period of from 0.1 to 10 hours to form aluminumorgano sulfur compounds, hydrolyzing said aluminum organo sulfurcompounds with an aqueous solution of a mineral acid and refining theliberated alkyl sulfur compounds.

3. The process of claim 1 wherein the temperature is from -150 C.

4. The process of claim 1 on which the process is carried out in thepresence of an inert diluent selected from the class consisting ofsaturated, aromatic and uaphthenic hydrocarbons.

5. The process of claim 1 wherein the mineral acids are selected fromthe class consisting of sulfuric and hydrochloric acids.

6. The process of claim 1 wherein the trialkyl aluminum istrioctylaluminum.

7. The process of claim 1 wherein the trialkyl aluminum istriisobutylaluminum.

8. The process of claim 1 wherein the trialkyl aluminum istrioctadecylaluminum.

No references cited.

1. A METHOD OF PREPARING ALKYL SULFIDES WHICH COMPRISES REACTING ANALUMINUM MERCAPTIDE OF THE FORMULA: